Electronically-controlled one- and two-qubit gates for transmon quasicharge qubits

TL;DR

This paper proposes a method to implement single- and two-qubit gates for protected quasicharge qubits in superconducting transmon devices using topological Josephson junctions, demonstrating robustness against charge noise.

Contribution

It introduces a new gate implementation strategy using topological superconductors and the $4 extpi$-periodic Josephson effect for quasicharge qubits, with simulation-based robustness analysis.

Findings

Gate operations are based on the same dynamical $4 extpi$-periodic Josephson effect.

Simulations show robustness against charge noise.

Proposes implementation using minimal Kitaev chains of quantum dots.

Abstract

Superconducting protected qubits aim to achieve sufficiently low error rates so as to allow realization of error-corrected, utility-scale quantum computers. A recent proposal encodes a protected qubit in the quasicharge degree of freedom of the conventional transmon device. Operating such a protected `quasicharge qubit' requires implementing new strategies. Here we show that an electronically-controllable tunnel junction formed by two topological superconductors can be used to implement single- and two-qubit gates on quasicharge qubits. Schemes for both these gates are based on the same dynamical $4\pi$-periodic Josephson effect and therefore have the same gate times and error characteristics. We simulate the dynamics of a topological Josephson junction in a parameter regime with non-negligible charging energy, and characterize the robustness of such gate operations against charge noise. Our results point to a compelling strategy for implementation of quasicharge qubit gates based on junctions of minimal Kitaev chains of quantum dots.